A wireless network, exemplified by a Long Term Evolution (LTE) network 100 is described in FIG. 1. Such a network comprises base stations, eNodeBs 102, 104, 106, which eNodeBs may provide coverage in one or more cells 103, 105, 107. The eNodeBs 102, 104, 106 each communicate with an MME 109 via an S1 interface. Further, the eNodeBs may communicate directly with each other via X2-interfaces. FIG. 1 further shows a user equipment (UE) 110 located in cell 107 and communicating wirelessly with eNodeB 106.
To be able to e.g. perform handover of UEs to neighbor cells, each eNodeB needs information about its neighbor cells. For this reason, each eNodeB maintains a neighbor relation table (NRT) for each cell it is managing. Each entry in such a table contains information that the eNodeB needs to know about a neighbor cell. For example, a first cell 107 has an NRT containing information about its neighboring cells 103 and 105.
Traditionally, NRTs have been built up using cell planning tools for coverage predictions before a base station is installed. Prediction errors, due to imperfections in map and building data, forced the operators to resort to drive and/or walk tests to control coverage regions and identify handover regions. This is significantly simplified in LTE by using a feature called automatic neighbor relation (ANR). The function of the ANR is to automatically add and remove neighbor relation entries to/from the NRT. Thereby, it is not necessary to perform drive tests. Instead, the NRTs are automatically built up and updated during use of the network.
In ANR, the UEs are adapted to decode and report cell identifications (cell ID) and other data of neighboring cells that it comes into contact with to its own base station, upon request. Taking the example shown in FIG. 1, UE 110 residing in cell 107 may, when it gets into contact with eNodeB 102 serving cell 103, report cell ID of cell 103 to eNodeB 106. For enabling the UE to get in contact with eNodeBs, each eNodeB broadcasts an identifying signature comprising its cell ID. In LTE, the cell ID may be a Physical Cell Identity (PCI). The PCI is not a unique ID and can therefore not be used to uniquely identify a neighbor cell. Therefore, the cell also broadcasts a globally unique cell identifier, such as Evolved Cell Global Identifier (ECGI), which is built up of a Public Land Mobile Network (PLMN) identity and a cell ID. The ECGI may later used by the eNodeB 106 to signal to the eNodeB 102 via the MME 109 over S1-interfaces. The ECGI is also used when acquiring via the MME 109 the IP address of eNodeB 102, which is used for establishing an X2 interface between eNodeB 106 and eNodeB 102.
The ANR may function in the following way, when the UE detects a cell that meets a configured reporting criterion, e.g. cell 102 in FIG. 2, the UE sends 2.1 a measurement report comprising a PCI of the cell 102, to the eNodeB 106. The UE may send the measurement report as a response to a report configuration of event based measurements or periodical measurements. The eNodeB 106 checks 2.2 whether the PCI is already known to the eNodeB or not. If the PCI is unknown to the eNodeB, the eNodeB 106 sends 2.3 a message to the UE to detect or decode ECGI for the cell 102. Thereafter, the UE sends 2.4 a measurement report to the eNodeB 106 comprising the detected ECGI of cell 102. The eNodeB then uses the ECGI to set up 2.5 a new neighbor cell relation with the cell 102. The established new neighbor cell relation is entered as a new entry in the neighbor relation table of cell 107/eNodeB 106. Further, the neighbor cell relation is reported to an O&M system of the wireless network, and an X2-interface is established between eNodeB 107 and eNodeB 103.
When using the ANR, there is a risk that a UE reports PC's and ECG's that has actually not been observed, i.e. faulty PC's or ECG's. This may be the case if a person has tampered with the UE, or if there for some reason is a fake or modified eNodeB in the wireless network. If a UE has reported a PCI or ECGI that has not been correctly received from a neighboring cell, a neighbor cell relation is established at the eNodeB the UE is connected to, which neighbor cell relation will not lead to any physical eNodeB controlling a physical cell. As a result, faulty X2 interfaces may be set up and/or handovers may try to be performed via a non-existing link resulting in failed handovers, lost calls, and UEs dropping form the network. Also, there is a risk that the NRT will be filled with faulty PC's and CGIs, which also may result in failed handover and UE drops. Eventually, a system breakdown may be the case.